This invention relates in general to microvalves for controlling the flow of fluid through a fluid circuit. In particular, this invention relates to an improved structure for an on-off microvalve that resists interference with the free movement of a displaceable member of the plate microvalve that might otherwise result from the presence of particulate contaminants contained in the fluid flowing therethrough.
Generally speaking, a micro-electro-mechanical system is a system that not only includes both electrical and mechanical components, but is additionally physically small, typically including features having sizes in the range of ten micrometers or smaller. The term “micro-machining” is commonly understood to relate to the production of three-dimensional structures and moving parts of such micro-electro-mechanical system devices. In the past, micro-electro-mechanical systems used modified integrated circuit (e.g., computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material), which were micro-machined to provide these very small electrical and mechanical components. More recently, however, other micro-machining techniques and materials have become available.
As used herein, the term “micro-machined device” means a device including features having sizes in the micrometer range or smaller and, thus, is at least partially formed by micro-machining. As also used herein, the term “microvalve” means a valve including features having sizes in the micrometer range or smaller and, thus, is also at least partially formed by micro-machining. Lastly, as used herein, the term “microvalve device” means a micro-machined device that includes not only a microvalve, but further includes additional components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be either micro-machined components or standard-sized (i.e., larger) components. Similarly, a micro-machined device may include both micro-machined components and standard-sized components.
A variety of microvalve structures are known in the art for controlling the flow of fluid through a fluid circuit. One well known microvalve structure includes a displaceable member that is supported within a closed internal cavity provided in a valve body for pivoting, axial, or other movement between a closed position and an opened position. When disposed in the closed position, the displaceable member substantially blocks a first fluid port that is otherwise in fluid communication with a second fluid port, thereby preventing fluid from flowing between the first and second fluid ports. When disposed in the opened position, the displaceable member does not substantially block the first fluid port from fluid communication with the second fluid port, thereby permitting fluid to flow between the first and second fluid ports.
In this conventional microvalve structure, the thickness of the closed internal cavity is usually only slightly larger than the thickness of the displaceable member disposed therein. Thus, relatively small spaces are provided between the displaceable member and the adjacent portions of the microvalve that define the closed internal cavity. This is done so as to minimize the amount of undesirable leakage therethrough when the displaceable member is disposed in the closed position. However, it has been found that when this conventional microvalve structure is used to control the flow of fluid containing solid particles (such as particulate contaminants that may be contained within the fluid), such particles may become jammed between the displaceable member and the adjacent portions of the microvalve that define the closed internal cavity. The jamming of such particles can, in some instances, undesirably interfere with the free movement of the displaceable member between the closed and opened positions. Thus, it would be desirable to provide an improved structure for a microvalve that resists interference with the free movement of a displaceable member of the microvalve that might otherwise result from the presence of particulate contaminants contained in the fluid flowing therethrough.